I was astonished to see a well known US brand which supplies a complete solar kit down to the inverter mains outlet use a rotary cam switch (typically seen on electrical panels) as a circuit breaker between the panels and the Inverter  (no internal arc quench in that design).

A simple rotary isolator between PV panels and inverter is a pretty well accepted way of doing things. It's only intended as an off-load isolator to allow work on the inverter. PV panels, unlike mains or large battery supplies, are incapable of producing large currents (it's limited by sunlight) - even into a dead short the maximum expected is 125% of normal output current. Oversize your PV d.c. cables by a little and no overcurrent protection is needed in a simple system.

Introducing batteries does introduce the potential for much nastier problems of course, but the charge controller would usually prevent backk-flow from the battery to the panel circuit.

   - Andy.

AJJewsbury said:

even into a dead short the maximum expected is 125% of normal output current

That's more than sufficient current to draw an arc, and sustain it for some considerable period of time (for example as an MC4 burns and disintegrates). WIth currents as low as 1-2 amperes !

In fact, if there is a fault, because they do happen, what is built into a solar PV system to enable someone to work on the system safely, or remove the arc etc.? Usually nothing!

For safe working on Solar PV, isolating at the inverter may stop current flow ... but what are the consequences if it didn't (say because there's a fault L+ to L- between the panels and in the inverter)? The only way to check for this, is to check for DC current flow with a DC current clamp meter at the point of disconnection, prior to disconnecting (because there's nowhere to "prove dead").

If not, these are the potential consequences: youtu.be/rkq1zwG9vLc

Years ago shortly before the reduction of FIT payments I did a C&G course on installing PV.  I received the course for free and at that it was not value for money. The lecturer thought that copper reduced in resistance when it got hot! The final exam could not be failed as if you got an answer wrong you tried again. All the attendees got one particular answer wrong until we pointed out that the answer we had all given was as per the course and supporting materials. The lecturer decided the "correct" answer was wrong and passed us all. 

Could I wire up a PV system following the course? Yes but I could do so before the course. Was I more competent and safer following the course ?No. 

If the course was an example of the level of training that we receive to install PV it is no surprise that there are poor installs. 

gkenyon said:

It's possible to cause an arc at 12 V DC

WRONG more homework needed GK

https://www.youtube.com/watch?v=5FXRuT6TU2U

you cannot draw an arc flash at 12 Vdc - nor at 15Vdc from a battery charger - its the Physics of the subject (very esoteric)

Here is an example with 2 batteries 24Vdc

https://www.youtube.com/watch?v=PV5oLPLUzrM

An arc flash can be sustained (out in the bush people have used coat hangers as welding rods)

Note the size of the Arc Flash and imagine that sustained in your faulty breaker or fuse holder

What will you do next ?

Are emergency procedures stuck to the wall for Joe Public and his Family?

Could I wire up a PV system following the course? Yes but I could do so before the course. Was I more competent and safer following the course ?No. 

If the course was an example of the level of training that we receive to install PV it is no surprise that there are poor installs. 

That is my experience too with the C&G EV course. I paid £354, expecting to learn something. It was a dire course, which, as you say, no one could fail. There certainly were people who should not have passed on my course, for example, the design part, which should have been done individually, was done as a group of 4, with little input from some, mainly due to their lack of understanding of the regs, but now they have the Certificate, and can be let loose on the public to install EV chargers.

gkenyon said:

For safe working on Solar PV, isolating at the inverter may stop current flow ... but what are the consequences if it didn't (say because there's a fault L+ to L- between the panels and in the inverter)? The only way to check for this, is to check for DC current flow with a DC current clamp meter at the point of disconnection, prior to disconnecting (because there's nowhere to "prove dead").

Indeed, a good point raised here - how to tell if a dc cable is dead.  Analogy the ubiquitous neon screw driver owned by every Leccie, automatically check for a live wire before intervention (also the bare knuckle test some believe is more reliable as your neon could fail)

So what is proposed here is that compulsory use of a Hall Effect clamp meter on solar cables before intervention.

BUT  the sad thing here which my OP highlighted is that we dont have any formal training worth a damn to promote theis level of Safety Training

Well said Alan - its this fashion today - started with the concept of dumbing down - that no one is judged as substandard.  Every one's a winner, nobody fails.

Perhaps someone will remind us here of the Political rush (10 + years ago) to coerce all Lecccies to take CnG course to become "Certified Competent Persons"  with the attraction being that this will disable all the cowboys from undercutting legitimate tradesmen who wish to offer professional services.  I remember there was a big fuss, because the Trade bodies ( set up by Gov Minister encouragement) and the Training purveyors were out to make a killing with course fees and subscriptions. Tales of woe abounded, with Tradesmen having to pay out £000's in fees and subs, only to find that the Gov did not follow through with legislation to ensure that only registered competent persons may offer electrician services.  The whole exercise became a huge damp squib and left thousands who had signed up for this accreditation without work as there was still nothing to stop Hairdressers" becomes "Leccies" overnight.  This is still the practice today AFAIK

Contrast this with the Gas Industry, where

It is illegal for someone who is not Gas Safe registered to fit a gas appliance or do other gas work
and then have the work checked by a Gas Safe registered engineer. Both parties would be breaking
the law

I appreciate the sentiment, but not quite, so to be accurate.

see The actual law for England and wales

"(1)No person shall carry out any work in relation to a gas fitting or gas storage vessel unless he is competent to do so.

(2) The employer of any person carrying out such work for that employer, every other employer and self-employed person who has control to any extent of such work and every employer and self-employed person who has required such work to be carried out at any place of work under his control shall ensure that paragraph (1) above is complied with in relation to such work.

(3) Without prejudice to the generality of paragraphs (1) and (2) above and subject to paragraph (4) below, no employer shall allow any of his employees to carry out any work in relation to a gas fitting or service pipework and no self-employed person shall carry out any such work, unless the employer or self-employed person, as the case may be, is a member of a class of persons approved for the time being by the Health and Safety Executive 

So

1) To be incompetent and work on gas is illegal.

And

2) No one shall offer themselves as an employee or employ someone to work on to work on gas unless at least one of them is a member of ( in effect Gas Safe)

There are a couple of points there -
1) An individual must be personally registered (employer or employee as applicable), and

2) It says nothing about folk who are neither employers nor employees.

Implying it is not exactly illegal under that act for example to fit your own gas fittings in your own caravan or something, but you must be competent to do so, which may be hard to demonstrate after something has gone wrong and come to the attention of the authorities,  but you certainly cannot do so by way of business without Gas Safe registration.

Amusingly the last survey I saw suggested these rules are also not observed everywhere either, and about 1/3 of things like boilers and cookers sold seem to install themselves magically without any sort of registration with the authorities ever occurring.

In slow time I'll see if I can find a link to that report.

I'm not sure it is a regulation model we should try to emulate.

Mike.

I agree it isn't but then where is the public information on what to look for ?

That absent  public profile again - Rather like how to check your tyres or oil, how to see if your electrics look dicky... It would not be hard. Perhaps it is a pity the old scary safety film unit is no longer in operation...

(I did wonder if British Public information films of kids being hit by trains and tractors or being accidentally locked in fridges and other such stuff were a side effect of the film classification system being quite strict, so frustrated British horror film makers ended up doing things like The Apaches or The Finishing line instead where they could let rip in the name of education. What they could have done with an unprotected  DC supply I wonder ? )

Mike

Rob Tes said:

WRONG more homework needed GK

I think we are at odds only in terminology, and I have tried to explain that in a previous post. To sustain the arc is difficult with 12 V due to the very short distance necessary. Easier with carbon or carbonised metal ... I never said you can weld with 12 V using arc welding sticks ... but arcs can be drawn for short periods with 12 V if you know how

youtu.be/Frk3M38mfl4

Perhaps rudeness is not necessary.

Rob Tes said:

you cannot draw an arc flash at 12 Vdc - nor at 15Vdc from a battery charger - its the Physics of the subject (very esoteric)

Yes, arc flash energy at 12 V may well be low, but an "arc" is not "arc flash" - they are two different things.

An arc can lead to arc flash (or not).